1. Field of the Invention
The present invention relates to a sheet feeding device and an image forming apparatus, and more particularly, to configurations of side edge regulating portions for regulating positions of side edges of sheets contained in a sheet containing unit.
2. Description of the Related Art
Nowadays, there is widely used an image forming apparatus such as a copier, a printer, and a facsimile, in which a sheet feeding device is used to feed a sheet to an image forming unit to form an image. As the sheet feeding device, there is a device, in which a plate-like sheet stacking unit for stacking sheets is provided in a sheet containing unit so as to be freely raised and lowered. When replenishing the sheets, the sheet stacking unit is lowered. When feeding the sheets, the sheet stacking unit is raised to move an upper surface of the stack of sheets to a position at which the sheets can be fed by a feed roller located above.
In this sheet feeding device, on the sheet containing unit, a trailing edge regulating portion, which regulates positions of upstream edges (hereinafter referred to as trailing edges) in a sheet feeding direction of the sheets stacked on the sheet stacking unit, is slidably provided so that sheets having different sizes can be contained in the sheet containing unit. Moreover, in the sheet feeding device, there is provided a side edge regulating portion, which regulates side edge positions of the sheets in a direction (hereinafter referred to as a width direction) orthogonal to the sheet feeding direction of the sheets. The side edges of the sheets are regulated by the side edge regulating portion, and the trailing edges of the sheets are regulated by the trailing edge regulating portion. In such a way, the position of each of the sheets is regulated at a predetermined position.
In such a conventional sheet feeding device, the sheet stacking unit is set at such a size that sheets with a maximum size, on which the image forming apparatus is capable of forming an image, are stacked on the sheet stacking unit. Therefore, in order that the side edge regulating portion can move in the width direction when the sheets with a smaller size than the maximum size are stacked on the sheet stacking unit, a cutout portion, which allows the movement of the side edge regulating portion, is formed in the sheet stacking unit. When the cutout portion is formed, strength of the sheet stacking unit is lowered, and accordingly, a formation amount of the cutout portion is limited. Along with such a limitation, a movement amount of the side edge regulating portion in the width direction is also limited. When the movement amount of the side edge regulating portion is limited, there is a risk in that side edge positions of small-size sheets, such as envelops and postcards, cannot be regulated by the side edge regulating portion. Therefore, as disclosed in Japanese Patent Application Laid-Open No. 2006-327805, there is a device, in which an auxiliary side edge regulating portion for regulating the small-size sheets is provided in the side edge regulating portion.
FIGS. 12A and 12B illustrate a configuration of a sheet containing unit of a sheet feeding device. In FIGS. 12A and 12B, side edge regulating members 510 and 511 are provided in a sheet storage 507 so as to be movable in the width direction, and a trailing edge regulating plate 514 is provided so as to be movable in the sheet feeding direction. A feed roller 501 feeds sheets P. On a downstream side of this feed roller 501 in the sheet feeding direction, a separation/feed roller (not shown), which separates the sheets fed by the feed roller 501 one by one, is provided. An intermediate plate 508 is provided in the sheet storage 507 so as to be capable of being raised and lowered. The sheets P are stacked on the intermediate plate 508, and the intermediate plate 508 presses the stacked sheets P against the feed roller 501.
On downstream ends of the side edge regulating members 510 and 511 in the sheet feeding direction, auxiliary side edge regulating members 512 and 513, which regulate edges of the sheets P having a small size, are provided so as to be pivotable about pivot shafts 512a and 513a serving as fulcrums. When regulating side edge positions of the sheets P having a small size, the auxiliary side edge regulating members 512 and 513 are moved to set positions indicated by the solid lines. When regulating side edge positions of the sheets having a regular size, the auxiliary side edge regulating members 512 and 513 are pivoted and moved to retreat positions indicated by the chain double-dashed lines.
In the sheet feeding device of such a comparative example, which includes the auxiliary side edge regulating members 512 and 513, it is only one-side surfaces 522 and 523 of the auxiliary side edge regulating members 512 and 513 that regulate the side edge positions of the sheets P in the auxiliary side edge regulating members 512 and 513. Therefore, when the auxiliary side edge regulating members 512 and 513 are located at the set positions, in regions indicated by the arrows 600 on the downstream side in the conveyance direction as illustrated in FIG. 12A, the auxiliary side edge regulating members 512 and 513 cannot be brought into contact with the sides edges of the sheets P and cannot regulate the side edge positions. That is, when setting the small-size sheets P, the side edge positions of the sheets P can be regulated by the auxiliary side edge regulating members 512 and 513. However, on the downstream side in the sheet feeding direction, guide-free regions (indicated by the dotted lines 532 and 533), in which the side edges of the sheets P cannot be regulated, are generated.
Due to the guide-free regions indicated by the dotted lines 532 and 533, the following problem occurs. Usually, in the sheet feeding device, a separation unit is arranged so as to separate the sheets, which are fed by the feed roller, one by one. In many cases, a separation pad and a separation roller are used for this separation unit. The separation pad and the separation roller separate the sheets from one another by friction force, and accordingly, there is a risk in that the separation pad and the separation roller may apply resistance to leading edges of the sheets fed thereinto and skew the leading edges of the sheets.
In general, in order to prevent the skew of the sheets by the separation unit, the side edge regulating members are arranged at positions as close to the separation unit as possible, to thereby regulate the sheets. However, when the guide-free regions are present, the skew of the sheets due to the separation unit cannot be regulated sufficiently. Hence, a frequency of the skew of the sheets due to the guide-free regions is increased, thus causing a problem in that the sheets cannot be fed stably.